1. Field of the Invention
The present invention relates to a premixing-type spray gun which mixes paint and compressed air inside an atomizing head and sprays the atomized mixture from a spray hole, and more particularly to such a spray gun having a paint supply amount control.
2. Description of the Prior Art
Premixing-type spray guns are well known. The conventional premixing-type spray gun is of such a construction that spraying air and paint are blown separately into a spray hole. Back pressure is applied to the outlet of the paint nozzle, and the higher the spraying pressure, the more the amount of sprayed paint is limited, having an influence on the finish of the paint-sprayed surface.
Generally, the paint nozzle of the spray gun is provided with a needle valve therein, and the amount of paint sprayed can be adjusted due to an increase in the sectional aperture area when the needle valve moves back. However, the needle valve does not sufficiently move back when the blow-out amount is limited. Therefore, the spray trigger is not fully pulled, but stopped at a mid-way point. The needle valve is provided at the rear thereof with a paint spray-amount control knob to which the trigger, that is, the rear end of the needle, can be pulled.
Thus the trigger cannot be fully pulled back, and the operability of the spray gun is poor.
The spray hole of the paint nozzle has its opening area limited by the end of the needle valve, and thus it is not assured that the spray aperature shape can be held in the correct shape. There is a great possibility that the spraying will vary. That is, if the needle valve end is positioned at the center of the circular spray hole, the paint is uniformly blown out from the circular clearance of the spray hole. However, when the end of the needle valve is placed eccentrically to either side of the circular spray hole, the blow-out clearance is not uniform, resulting in an irregular blow-out.
Hence, the spray hole should, desirably, be so formed that the paint is blown out while the correct blow-out aperture is being held with the needle valve positively let back.